Transformer and method of making same



N. F. GAKLE Data 31 1933,

TRANSFORMER AND METHOD OF MAKING SAME" Filed Jan. 29, 1929 2Sheets-Sheet l Oct. 31, 1933. w GAKLE 1333 140 TRANSFORMER AND METHOD OFMAKING SAME Filed Jan. 29, 1929 2 Sheets-Sheet 2 affozueq m v PatentedOct. 31, 1933 TRANSFORMER AND METHOD OF MAKING F. Gakle, Bay City, Mich,assignor to Electric Company, Bay City, Mich, a

Wendolyn Kuhlman SAME corporation of Michigan Application January 29,1929. Serial No. 385,888 11 Claims. (01.175-356) This invention relatesto an electric transformer and a method of making the same.

It is an object of the invention to improve the magnetic circuit ofelectric transformers and to facilitate the assembly of the laminationsof which this magnetic circuit is composed.

Another object of the invention is to provide a magnetic circuit ofreduced weight, as compared with the magnetic circuit of knowntransformers of similar capacity, and to assemble for this purpose thelaminations of the core in loop form so that the major part of the corematerial is. at the short perimeter of the loop.

Another object of the invention is to provide a method for assemblinglaminations which will facilitate the positioning of the transformerwindings in proper relation to the core, and to provide greaterfacilities for the insulation of the windings from the core.

It is also an object of the invention to provide a novel method ofassembling laminations for a transformer core in such manner that theycan readily be deformed to facilitate the windings of the coils in loopsof the core, and may be returned again to the position in which theyconstitute closed magnetic circuits.

It is, further, an object of the invention to simplify the contour andshape of the laminations of which the core and yoke is composed, and toeliminate the great amounts of waste and scrap which heretofore wereunavoidable in the formation of these cores.

With these and numerous other objects in view, the invention isdescribed in the following specification in which reference is made tothe accompanying drawings.

In the drawings:

Fig. 1 is a side elevation of an assembled transformerproduced inaccordance with the present invention.

Fig. 2 is partly a top plan view and partly a horizontal section of thetransformer core, the transformer coils being omitted.

Fig. 3 shows on a different scale a sheet of metal in plan view toillustrate the method of cutting the various laminations.

Fig. 4 is a plan view of one of the short laminations.

Fig. 5 is a plan view of one of the longer laminations.

Fig. 6 is an edge view showing one of the laminations bent to shape.

Fig. 7 is a fragmentary sectional view taken on the line 'I'l of Fig. 8.

Fig. 8 is a front view of a form to which the core is secured to permitthe application of the coil, two of the core loops being shown closed,the others being shown in opened position, with means for holding thelaminations in open position.

Fig. 9 is a fragmentary transverse sectional view through one of theform discs.

In transformer practice as formerly followed by all manufacturers themagnetic circuit consists of rectangular or L-shaped pieces assembled invarious forms, some with single circuits, others with multiple circuits,but all functioning in the I same manner, which is to form a closedmagnetic circuit around a coil which is placed on a part of saidmagnetic circuit, this part is called the core and the remaining part iscalled the shell or yoke.

Now in order to project the core section that is within the coil aroundthe outside thereof, it is necessary to have part of this core close tothe coil and other parts progressively more distant, the side which isclose to the coil being termed the short perimeter, while the sidefarthest from the coil is termed the long perimeter of the magneticcircuit, and it is in these perimeters that the important feature ofthis invention resides. In my construction the short perimeter oradjacent surface of the coil is more thoroughly used than heretoforethereby causing more of the core section to be projected around the coilon its short perimeter, leaving progressively less material to beprojected around the coil as the core progresses away from the coil andtowards the long perimeter.

The net result is a reduction in weight of magnetic material for a givencoil enclosure, this in turn results in lower core loss and alsopresents the designer with means whereby he can maintain formerperformance, and reduce the weights very materially of the magneticcircuit, the electrio circuit, and theinsulation. The cross-section ofthe assembled core also is utilized economically to a higher degree thanheretofore, since the portion of the core having the smaller perimeterand being closer to the coil is broader than the portion of the coreadjacent the outer perimeter.

For this purpose the core sections of the transformer are each composedof strips which are bent into loop shape, the loops formed of aplurality of strips nested one in the other, and being preferably ofelongated shape to receive the coil therein. A plurality of thesesections are then assembled with one part of the loop in the cen-' tralpart of the coil of which the transformer is built up, and .the otherpart of the loop on the outer side of the coil. To reduce thecross-section or the core portions adjacent the central part or the coilthe cross-sections of the core parts gradually decrease in directiontowards the axis of the coil, and they also decrease in directiontowards the outer perimeter of these individual loop core sections.

This form of cross-section is produced by building up the core ofindividual laminations or strips, the width 01 which decreases in eachcore portion in proportion to the approach or the respective strip tothe outer perimeter of each loop, so that for instance the outer.perimeter of each loop is formed by the narrowest strip which must bethe longest, while the inner perimeter of the loop is formed by thewidest strip, which naturally also will be the shortest of all--01 thestrips of which the core is being built up.

It has been round that the proper variation 0! the length and of thewidth of the different strips can best be produced by cutting them froma sheet 0! metal having two parallel sides and two sides which areconverging. The form of this sheet, therefore, may be that or atrapezoid. The longer and narrower strips are cut from near the base ofthe trapezoid, the width of the strips increasing coincidentally withthe decrease or their length when progressing from the base or the sheetin direction towards the opposite parallel side.

This method of cutting the strips has been indicated diagrammatically inFig. 3, in which 1 indicates a trapezoidal shaped sheet 01 metal havingthe base 2 and the opposite parallel side 3, while the two non-parallelsides are indicated at 4 and 5 and are shown here as sides oi a regulartrapezoid forming angles with the base 2. This sheet 1 is thensubdivided by cuts 6 extending parallel to the base, whereby strips '7or unequal length are produced. The strips cut from adjacent the base 2are considerably longer than those cut from that portion or the sheetwhich is adjacent the opposite parallel side 3. These strips 7, however,also are cut of nonuniform width, each striphaving equal widththroughout its length, but the longer strips being narrower than theshorter ones. All of the strips 7 produced in this manner are similar toeach other but have different length at the base line and also diflerentheight.

The strips may then be piled on each other in such manner that theshortest and widest strip '7 is at the bottom of the pile, the otherstrips being superimposed so that the narrowest and longest stripconstitutes the top of the pile. This entire stack of strips may then beheld together in a suitable way by wires or the like, not illustrated inthe drawings. This stack is then bent into the form of a loop, thebending force being exerted in a direction at right angles to the planesof the greater transverse dimension of the strips or laminae, so thatthe greater transverse dimensions of the laminae will be, in thecompleted core, substantially concentric with the coil instead of radialwith respect to the coil as heretoi'ore and the narrowest and longeststrip will be located at the outer perimeter oi. the loop, while theshortest and broadest strip will constitute the inner perimeter, theintermediate strips by their assembly forming the body or the loop. Theopening or the loop may be circular or 01' any other desired formation,corresponding preferably to the cross-sectional contour oi. the coil tobe placed in the core window 8. The ends or the individual strips areplaced in overlapping relation, as clearly shown at 9 in Fig. 6, of thedrawings. The proportion of the parts is selected in such manner thatthe extent or the overlap 9 is approximately the same with all oi. thestrips or gradually converging either way.

It will, iurthermore, be noted that owing to this overlap of theprojecting ends and the interlinkage of these ends with the strips, theleg 10 of the loop containing two overlapping portions 9 of each stripwill have a thickness about twice as great as the other leg 11 in whichthis section is formed of the central portions of the strips only.

The sections having been assembled and bent as above described are heldtogether by suitable elements, such as clamps or steel wire (not shown)to prevent their deformation, and in this condition the various sectionsare annealed. The bending oi the individual strips is somewhat injuriousto the electric characteristic of the iron, and this detrimental eflfectof the bending operation is eliminated by the annealing operation whichtakes place after the strips have been bent to shape.

Several of these core sections S each composed of a plurality of strips7 bent into loop shape, may then be assembled to form a star orcrossshapedtransiormer core 0, Fig. 2. The central part or the core willbe constituted by the inner legs ll of the sections S, which inner legsin cross-section are reduced towards the outer perimeter of each loop.This assembly is indicated in Fig. 2, where it is shown that the innerlegs 11 are placed in close relation to each other, leaving between themand the outer legs of the same section, a window through which thetransformer coil 12 may be placed.

In order to facilitate the winding of the coil 12 in the assembled core,the outer legs 10 ot the section S are opened, this is accomplished bymeans of a suitable clamping device such as shown in Figs. 7 and 8 ofthe drawings, which comprises spaced apart disk members 13 convex shapedand so proportioned that the opening stresses ,do not exceed the elasticlimit, these members are connected together by means of the centrallydisposed bolt 14, which projects through the center of the core. Afterthe assembled sections are placed in position in the clamping device,the ends of the laminations are bent outwardly against the face 0! themembers 13 to form open loops in which the coil may be wound, thelaminations being held in this position by means of clamps comprisingspaced apart bolt members 15, the upper ends or which are hook shaped toaccommodate a cross member 16, the lower end of the bolts beingpreferably threaded and are provided with conventional nuts foradjustment, a suitable crank (not shown) being provided for turning thedevice so that the wind- 35 ing of the coil is facilitated. After thecoil 12 of the transformer has been positioned, the portions of the legswhich were opened are returned again to their original position, andsecured therein, and in that way the section is 40 closed.

It will therefore be obvious that for a given core section and requiredwindow space for the coil that the weight of the iron copper andinsulation is materially reduced, it Iurther serves to eliminate scrapwhich is unavoidable with L-shaped laminations or laminations consistingof a pair of spaced legs, and it is obvious that also the production ofthe core irom these trapezoid shaped strips'eliminatesthe necessity ofto obtain satisfactory results with less material or better results withthe same amount of material that went heretofore into the constructionof the cores.

The assembly of the strips also can be carried out in less time and withless labor than the assembly of laminations having irregular shapes. Thereduction of the cross-section of the core in width towards the centerof the transformer also induces a more uniform and better radiation ofheat, because joints are eliminated and better edge presentation tocooling oil is provided. The assembled core is more accessible forrepairs, and the opening of the loop where it should become necessary,would require less effort than the separation of sheets which areinserted between the free ends of the legs of laminations as has beendone in standard practice.

The coils are wound into the loops after they have been opened to thedesired extent, thereby removing the space factor and inducing a greaterrigidity than was known heretofore. The provision of these loops alsomake it possible to place insulating material against the laminations onthe irmer perimeter, permitting the insulating material to projectbeyond the coils.

What I claim is:-

1. The method of making the magnetic core of a transformer, consistingof forming a plurality of loops each composed of laminae, or strips bentto required form, assembling the loops so that their inner legs areproximate to one another, opening the outer legs of the loops, windingthe coil on the inner legs of the loops through the open outer legsthereof and restoring the outer legs of the loops to their initialclosed condition.

2. The method of making the magnetic core of a transformer, consistingof forming a plurality of loops each composed of laminae, bent so thatthe minor portion of the metal is at the long perimeter thereof,assembling the loops so that their inner legs are proximate to oneanother, opening the outer legs of the loops, winding the coil on theinner legs of the loops through the open outer legs thereof, andrestoring the outer legs of the loops to their initial closed conditionand arranging the endsof each lamina: in overlapping relation.

3. The method of forming a loop, for the magnetic core of a transformer,consisting in arranging a plurality of strips in superimposed relationand bending said strips so that the inter- 1 mediate portions of thestrips form an inner core leg and the outer portions of the strips forman openable outer core leg, arranging the ends of each strip inoverlapping relation, and annealing the bent strips.

4. The method'of making the magnetic core of a-transformer, consistingof forming a plurality ofloops each composed of strips bent so that theminor portion of the metal is at the long perimeter of the loop, and sothat the inter mediate portions of the strips form an inner core leg,and the outer portions of the strips form an openable outer coreleg,"arranging the ends of each strip in overlapping relation. and thenannealing the bent strips.

5. A transformer core comprising an assembly of loops composed oflaminae of progressively varying widths and lengths, said laminae beingbent in the direction at right angles to the planes of the greatertransverse dimensions of the laminae, and so that the minor portion ofthe metal is at the long perimeter of the loop.

6. A core as claimed in claim 5, in which the intermediate portions ofthe lamina: form a continuous inner leg and the end portions of thelamina: form an openable outer leg.

- '1. A core as claimed in claim 5, in which the intermediate portionsof the lamina form a continuous inner leg and the end portions of thelamina: form an openable outer leg, and the end portions of each lamina:being arranged in overlapping relation.

8. A transformer core comprising a plurality of loops each composed oflamina: of varying widths and lengths, producing in the complete core across section of substantially triangular shape with the major part ofthe metal at the short perimeter of the loop, and a coil inter-linkedwith the loop of the core.

9. A transformer core comprising a plurality of loops each composed oflaminae bent in the direction at right angles to the planes of thegreater transverse dimensions of the laminae, said laminae progressivelydiminishing in width from the inner to the "outer perimeter of the loop.

10. A transformer having the cross section of its core divided intosections, each of said sections being composed of lamina: or strips, thenarrowest and longest strips being at the center of the combined crosssection, said strips gradually widening as they approach the rim of thecoil opening.

11. A transformer having the cross section of its core divided intosections, each of said sections being composed of lamina or strips ofvarying widths and lengths, the narrowest and longest strips being atthe center of the combined cross section, said strips gradually wideningas they approach the rim of the coil opening.

WENDOLYN F. GAKLE.

